import sys
import os
from mido import MidiFile, MidiTrack, merge_tracks

def convert_to_type0(input_filepath):
    """
    Converts a MIDI file to Type 0 and saves it with "_0" appended to the original filename.
    
    Parameters:
        input_filepath (str): Path to the input MIDI file.
    
    Returns:
        output_filepath (str): Path to the converted Type 0 MIDI file.
    """
    try:
        # Load the original MIDI file
        midi = MidiFile(input_filepath)
        print(f"Loaded MIDI file: {input_filepath}")
        print(f"Original MIDI type: {midi.type}")
        print(f"Number of tracks: {len(midi.tracks)}")
        
        # Merge all tracks into one
        merged_track = merge_tracks(midi.tracks)
        print("Merged all tracks into a single track for Type 0 MIDI.")
        
        # Create a new MIDI file with one track
        type0_midi = MidiFile()
        type0_midi.type = 0  # Explicitly set to Type 0
        type0_midi.ticks_per_beat = midi.ticks_per_beat  # Preserve timing
        
        type0_midi.tracks.append(MidiTrack(merged_track))
        
        # Prepare output file name
        base, ext = os.path.splitext(input_filepath)
        output_filepath = f"{base}_0{ext}"
        
        # Save the new Type 0 MIDI file
        type0_midi.save(output_filepath)
        print(f"Type 0 MIDI file saved as: {output_filepath}")
        
        return output_filepath

    except Exception as e:
        print(f"An error occurred: {e}")
        sys.exit(1)

def main():
    if len(sys.argv) != 2:
        print("Usage: python midi_to_type0.py <input_midi_file>")
        sys.exit(1)
    
    input_filepath = sys.argv[1]
    
    if not os.path.isfile(input_filepath):
        print(f"Error: File '{input_filepath}' does not exist.")
        sys.exit(1)
    
    convert_to_type0(input_filepath)

if __name__ == "__main__":
    main()